Many pharmaceuticals are prone or potentially subject to misuse or abuse when the intended dosing instructions are ignored and/or the written instructions are disregarded. For example, it is well known that sustained-release narcotics, such as OXYCONTIN® ER tablets (supplied by Perdue Pharma), are prone to abuse and misuse when their dosage units are broken, chewed, crushed, dissolved, or otherwise disrupted, rather than being taken whole as intended. Other narcotic and analgesic drugs are liable to similar misuse. Other types of drugs, including those which are not amenable to abuse, may, nonetheless, be inappropriately used. Such inappropriate use can lead to adverse reactions in persons so using the drugs and can give rise to adverse reactions and even death. One example of this is the inappropriate use of metformin sustained-release (e.g., GLUCOPHAGE® XR, metformin hydrochloride extended-release tablets supplied by Bristol-Myers Squibb), a common diabetes drug. If metformin sustained-release is chewed, or the tablets otherwise disrupted prior to ingestion, rather than the tablets being swallowed whole, dangerous lowering of a person's blood glucose level may result. Very large numbers of pharmaceuticals may be inappropriately ingested in this way and a method for reducing or eliminating the undesired effects has long been desired.
Many pharmaceutical products, which have been introduced into the pharmaceutical market in an immediate-release tablet or capsule form, have subsequently been reformulated into a sustained-release form. The sustained-release form has provided the advantages of more convenient dosing schedules, increased patient compliance, more even blood levels, improved therapeutic activity, or others. Typically, the dosage of active pharmaceutical ingredient in these sustained-release formulations is greater than the dosage of the corresponding immediate-release formulation. This presents the danger of “dumping” in which the sustained-release mechanism fails, either intentionally or unintentionally, so that potentially dangerous dosages of the active pharmaceutical ingredient (agonist) are delivered to the patient causing dangerously high blood levels of the agonist. For example, the Physicians' Desk Reference (PDR), 56th Edition, states for GLUCOTROL®. XL Extended Release Tablets (supplied by Pfizer), under “Information for Patients”, that “Patients should be informed that GLUCOTROL XL Extended Release Tablets should be swallowed whole. Patients should not chew, divide, or crush tablets.” For the product RITALIN-SR® (supplied by Novartis) under “DOSAGE AND ADMINISTRATION”, it is written, “Ritalin-SR tablets must be swallowed whole and never crushed or chewed.” For OXYCONTIN® ER tablets (supplied by Perdue Pharma) there has been much recent controversy and numerous published reports of narcotic abuse through mechanical disruption of the sustained-release mechanism thereby enabling the abuser to receive a relatively larger immediate dose of narcotic.
Some attempts at providing dosage forms for preventing abuse of narcotics have been offered by the prior art. For example, U.S. Pat. No. 4,457,933, Gordon et al., discusses both oral and parenteral abuse of strong analgesics, such as oxycodone, propoxyphene and pentazocine. Gordon et al. discuss oral administration of compositions containing specific ratios of oxycodone to naloxone, a narcotic antagonist. According to Gordon et al., the antagonist, naloxone, is supplied in an amount to deter either oral or parenteral abuse of an analgesic without substantially affecting the analgesic activity. Gordon et al., therefore, contemplates that the antagonist be absorbed into the blood in normal use along with the analgesic.
U.S. Pat. No. 5,375,957 in the name of Kaiko et al. recognizes that oral and parenteral abuse of oral opioid formulations can occur by self-administration of more than the prescribed oral dosage. Kaiko et al. discusses an appropriate ratio between analgesic agonist and antagonist in such dosage forms to ensure analgesic efficacy is maintained. Thus, Kaiko et al. contemplates that the antagonist be absorbed into the blood in normal use along with the agonist. Kaiko et al. distinguishes itself over prior art that teaches inclusion of antagonists in oral opioid analgesic dosage forms, which are themselves not orally active, but which counteract the analgesic effects of the opioid upon parenteral administration. As an example, Kaiko et al. describes the commercially available combination of pentazocine and naloxone, wherein the amount of naloxone does not interfere with the pentazocine upon oral administration. As such, it is understood that the antagonist would still be absorbed into the blood in normal use along with the agonist, but would not provide any pharmacological activity.
Pharmaceutical dosage forms that permit absorption into the blood of an antagonist are inefficient because of the resulting potential to hinder the activity of the agonist during normal use. This limits the amount of antagonist that can be used. This also limits the potential amount of antagonist activity that can be incorporated into the dosage form to less than the amount of activity that will substantially inhibit the agonist activity. Even if, as in Gordon et al., the antagonist, naloxone, can be present in amounts that are not orally active, this may not be possible or desirable with antagonists for other drugs. Also, even if the antagonist is not orally active, it may still be absorbed by the blood and impact the patient during normal use of the dosage form. Additionally, as in Gordon et al., if the antagonist is inactive with oral use then it cannot provide protection against dumping of the agonist if the sustained-release tablet is mechanically disrupted. Furthermore, lack of oral activity may not deter oral abuse.
There remains a great need for dosage forms which can minimize or eliminate the effects of abusive or otherwise inappropriate use of pharmaceuticals. A need exists for dosage forms which may be employed for the delivery of a wide range of drugs and which do not require the coadministration of a separate second pharmaceutically active dosage unit in addition to the desired pharmaceutical. Dosage forms which ensure the safe administration of drugs without unnecessarily loading the bloodstream of a person taking the drug with additional dosage units are objects of this invention. A further object is to provide dosage forms which block an avenue of abusive value to a person in possession of the dosage unit. Other objects will become apparent from a review of the present specification.